Posted by daestrom on November 17, 2011, 9:50 pm
On 11/16/2011 18:32 PM, m II wrote:
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> Johny B Good wrote:
>> A modern alternator removes the need for laminated magnetic core
>> materials from the bit that rotates, allowing for solid steel poles and
>> a co-axially wound field coil. A design change that permits
>> significantly higher rotational speeds compared to the armature of a
>> dynamo.
> I beg to disagree.
> It could be argued that laminated armatures are far stronger than one
> piece, cast versions. Each lamination has a hardened 'skin' on it that
> forms during the manufacturing process.
> They are certainly more vibration resistant than cast pieces. The reason
> they are cast is one of economics. It's cheaper than assembling laminations.
> As for the co-axially wound field, it would make no difference. The
> reason alternators can spin so high is the fact that it's the *field*
> spinning instead of the main windings. The rotor wire is a lot smaller
> than that of generator, resulting in a great reduction of centrifugal
> force.
Well I disagree with your disagree statement.
It isn't a question of how strong the steel is, it's a matter of how the
winding is placed.
In conventional DC generator, the windings are placed axially in slots
with insulation and wedging. This wedging fails at high speeds,
allowing the winding to spill out of the slot.
Also the turns at each end of the rotor where the wire exits one slot,
travels part way around the rotor and enters another slot is subject to
failure. In tiny machines, the wire is self-supported. In larger
units, the end turns are banded with insulation and steel wire to hold
them inward against the centrifugal forces. Spin it fast enough and
when that support fails, the end turns bow outward, contact the stator
iron and get destroyed.
Because the alternator winding is mounted in between the two iron rotor
pieces, and they each have about 14 steel teeth bent towards the
opposite piece, they provide a very strong case to hold the copper
windings inside. The 'teeth' are about 3/8 inch by 1/2 inch square
steel bar (or larger). When assembled, there is very little space
between them and the wire is crossing the gap at nearly right angles,
not lined along the gap like the slots in a DC generator. (The steel
pieces are forged and heat treated, not cast, BTW)
DC generators are also limited in speed by the commutator construction.
All the bars are held in place with just a couple of bands, one on
each end (on small machines, sometimes steel wire wrapped over the bars
with insulation). At high speeds these bands can stretch from the
extreme forces. This lets the bars slip in relation to one another.
Even if the bars don't come out completely from under the banding, once
a bar slips the brushes get chopped off by the high bar like a buzz-saw
in a matter of seconds.
These problems are also eliminated with an alternator and replaced with
single piece slip rings that are made of one piece (again, much stronger
construction).
daestrom
Posted by m II on November 18, 2011, 12:11 am
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daestrom wrote:
> On 11/16/2011 18:32 PM, m II wrote:
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>> Hash: SHA1
>>
>> Johny B Good wrote:
>>
>>> A modern alternator removes the need for laminated magnetic core
>>> materials from the bit that rotates, allowing for solid steel poles and
>>> a co-axially wound field coil. A design change that permits
>>> significantly higher rotational speeds compared to the armature of a
>>> dynamo.
>>
>>
>> I beg to disagree.
>>
>> It could be argued that laminated armatures are far stronger than one
>> piece, cast versions. Each lamination has a hardened 'skin' on it that
>> forms during the manufacturing process.
>>
>> They are certainly more vibration resistant than cast pieces. The reason
>> they are cast is one of economics. It's cheaper than assembling
>> laminations.
>>
>> As for the co-axially wound field, it would make no difference. The
>> reason alternators can spin so high is the fact that it's the *field*
>> spinning instead of the main windings. The rotor wire is a lot smaller
>> than that of generator, resulting in a great reduction of centrifugal
>> force.
>>
>
> Well I disagree with your disagree statement.
>
> It isn't a question of how strong the steel is, it's a matter of how the
> winding is placed.
>
> In conventional DC generator, the windings are placed axially in slots
> with insulation and wedging. This wedging fails at high speeds,
> allowing the winding to spill out of the slot.
>
> Also the turns at each end of the rotor where the wire exits one slot,
> travels part way around the rotor and enters another slot is subject to
> failure. In tiny machines, the wire is self-supported. In larger
> units, the end turns are banded with insulation and steel wire to hold
> them inward against the centrifugal forces. Spin it fast enough and
> when that support fails, the end turns bow outward, contact the stator
> iron and get destroyed.
>
> Because the alternator winding is mounted in between the two iron rotor
> pieces, and they each have about 14 steel teeth bent towards the
> opposite piece, they provide a very strong case to hold the copper
> windings inside. The 'teeth' are about 3/8 inch by 1/2 inch square
> steel bar (or larger). When assembled, there is very little space
> between them and the wire is crossing the gap at nearly right angles,
> not lined along the gap like the slots in a DC generator. (The steel
> pieces are forged and heat treated, not cast, BTW)
>
> DC generators are also limited in speed by the commutator construction.
> All the bars are held in place with just a couple of bands, one on each
> end (on small machines, sometimes steel wire wrapped over the bars with
> insulation). At high speeds these bands can stretch from the extreme
> forces. This lets the bars slip in relation to one another. Even if the
> bars don't come out completely from under the banding, once a bar slips
> the brushes get chopped off by the high bar like a buzz-saw in a matter
> of seconds.
>
> These problems are also eliminated with an alternator and replaced with
> single piece slip rings that are made of one piece (again, much stronger
> construction).
>
> daestrom
Well I disagree with your disagree with my disagree statement.
Not because you're wrong, but because I'm just contrary. Everything you
say is true, but you can't discount the difference in centrifugal force
between a field winding and a main current carrying one. The weight per
unit difference alone would be enough to let the alternator spin three
times as fast as a generator.
That's my story, and I'm sticking to it.
mike
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Posted by Morris Dovey on November 14, 2011, 7:49 pm
On 11/14/11 12:28 PM, Rick wrote:
> I've actually come across an online instruction manual for the Philips
> MP1002CA 230v/180W hot air generator, manufactured back in 1951, I'm
> guessing that a version made now, 60 years on, would be considerably
> more efficient?
> <http://www.oldengine.org/members/croft/images/MP1002CA.pdf>
It was one of those things that was better in concept than in practice.
There are a couple of people who've managed to get their hands on these
things, and they all say the darned things have more value as souvenirs
than as generators.
I think we /can/ build much more efficient Stirling engines, but it'll
require some serious work to develop the technology. Most of the people
now involved are (re)inventing from what they can see in their rear-view
mirror...
--
Morris Dovey
DeSoto Solar
http://www.iedu.com/Solar/
Posted by Morris Dovey on November 14, 2011, 7:35 pm
On 11/14/11 12:03 PM, Rick wrote:
>>
>> I want to buy a Stirling engine in the 1-2 hp range suitable for using
>> in a solar heat (~750F) context. Do you have, or can you find, a link
>> to a product with a price comparable to internal combustion engines in
>> that power range?
> I'm sorry Morris but other than replying to the post that apparently
> Stirling engines do appear to have at least some practical use in the
> conversion of solar energy to electricity, I have no involvement
> whatsoever, however this engine manufacturer was mentioned in the Wiki
> article.
> <http://www.infiniacorp.com/application.html>
Interesting, but it doesn't appear to be in the same price class as
Briggs & Stratton (et al). I've done a lot of searching, but it doesn't
appear that anyone is offering consumer-affordable products.
Still looking - and hoping (but not holding my breath).
--
Morris Dovey
DeSoto Solar
http://www.iedu.com/Solar/
Posted by harry k on November 14, 2011, 7:55 pm
> On 11/14/11 12:03 PM, Rick wrote:
> >> I want to buy a Stirling engine in the 1-2 hp range suitable for using
> >> in a solar heat (~750F) context. Do you have, or can you find, a link
> >> to a product with a price comparable to internal combustion engines in
> >> that power range?
> > I'm sorry Morris but other than replying to the post that apparently
> > Stirling engines do appear to have at least some practical use in the
> > conversion of solar energy to electricity, I have no involvement
> > whatsoever, however this engine manufacturer was mentioned in the Wiki
> > article.
> > <http://www.infiniacorp.com/application.html>
> Interesting, but it doesn't appear to be in the same price class as
> Briggs & Stratton (et al). I've done a lot of searching, but it doesn't
> appear that anyone is offering consumer-affordable products.
> Still looking - and hoping (but not holding my breath).
> --
> Morris Dovey
> DeSoto Solarhttp://www.iedu.com/Solar/
Yep. The Stirling does have some hope of practical use. I will make
a prediction that if it ever does, it will be in a very limited
application. For sure beats out the wackos pushing "the Amazing Air
Car", the "Psuedoturbine" and the like :)
Harry K
XML site map
> Hash: SHA1
> Johny B Good wrote:
>> A modern alternator removes the need for laminated magnetic core
>> materials from the bit that rotates, allowing for solid steel poles and
>> a co-axially wound field coil. A design change that permits
>> significantly higher rotational speeds compared to the armature of a
>> dynamo.
> I beg to disagree.
> It could be argued that laminated armatures are far stronger than one
> piece, cast versions. Each lamination has a hardened 'skin' on it that
> forms during the manufacturing process.
> They are certainly more vibration resistant than cast pieces. The reason
> they are cast is one of economics. It's cheaper than assembling laminations.
> As for the co-axially wound field, it would make no difference. The
> reason alternators can spin so high is the fact that it's the *field*
> spinning instead of the main windings. The rotor wire is a lot smaller
> than that of generator, resulting in a great reduction of centrifugal
> force.